1. Field of Invention
The field of invention is computer architecture, particularly as applicable to communications controllers. CCITT protocols supported by Open Systems Interconnection (OSI) standards are considered a basis for the architecture underlying the present invention, although other protocols such as SNA could be equally supported. Specific device areas to which this invention may be beneficially applied include network interfaces, front end communication controllers for large systems and telecommunications switching nodes. This architecture is also applicable to network gateway implementations and protocol conversion.
2. Prior art
Use of programmable communications controllers to concentrate signal traffic between multiple communications lines and data processing equipment is not per se new. U.S. Pat. Nos. 3,863,226; 4,156,796; 4,156,932; 4,188,665; 4,328,543; and 4,484,263 disclose various methods of implementing such controllers, using commercially available general purpose microprocessors as processing engines, and "off-the-shelf" asynchronous receiver and transmitter (USART) devices.
Related patent application for "Real Time Digital Signal Processing..", cross-referenced above, discloses a hardware assist mechanism to handle the media access (MAC) layer for protocol flexibility. It recognizes a need for special purpose terminal equipment to support various types of information transmission needs of the future.
However, we are unaware of any recognition in the art of the particular problem addressed here; i.e. the need for dealing specifically with header and frame processing functions repeatedly encountered in layered communication protocols, at speeds and protocol levels adequate for present and future needs in high throughput real time communication. This problem is solved presently by providing special purpose circuits and associated instructions dedicated to speeding up handling of such repeatedly encountered header and frame processing functions at all levels of todays layered protocols (e.g. OSI standards). These circuits and instructions include implementational features permitting execution of associated header and frame processing operations in single machine cycles, with flexibility suited to accommodating similar operations at the physical, data link, network, transport, session, presentation and application layers of OSI and other layered communication protocols. Those skilled in the art will recognize that the prior art above uses communication control processors which are directed to the handling of link access functions and generally rely upon more powerful processors in intermediate or host systems for processing communication protocol layers above the link access level.
More specifically, our present understanding is that contemporary general purpose microprocessors and digital signal processors, as used to implement processing engines or CPU (Central Processing Unit) elements in prior art communication controllers, were not considered suitable for handling support functions associated with processing of header and frame information in layers of today's layered communications protocols above the link control or media access layers; nor has the art apparently recognized that a need for such support exists at the link access level. We have found however that such support is needed for efficient utilization of high speed media (T-1, T-2, fiber optics, etc.). Stated otherwise, we have recognized that processing loads imposed by present and future high speed links are such that, without offloading of header and frame process functions above the link control layer, I/0 and processing bottlenecks would inevitably occur, with consequent blockage or reduction of throughput speeds limiting effective media usage.
Of course, there have been major advances in areas related to this work; e.g. improvements in microprocessor and VLSI technologies applicable to communication controls, advances in protocols per se and improvements in parallel processing. Although these might tend to alleviate the presently recognized problem, they do not provide the more effective and complete solution to which the present invention is directed.